1. Field of the Invention
The present invention relates to an image encoding apparatus for compression encoding of image signal and an image recording apparatus for recording image signal.
2. Related Background Art
Conventional image recording apparatus, for example still video camera, is based for example on analog signal recording on floppy disks or recording of digital image data, compressed by fixed length encoding, in semiconductor memory cards. The fixed length encoding means a compression encoding in such a manner that the amount of compressed codes of an image frame becomes equal to a predetermined value.
Such conventional image signal recording methods can guarantee the number of images recordable per recording medium, because the capacity thereof required for recording image data of an image frame is predetermined.
However, for example in a digital still video camera employing image data compression with a fixed length encoding method, the rate of compression can empirically be only increased to the order of 8 bit/pixel, including the luminance and the color information, in order to guarantee the quality of compressed image for various image data, for example those involving fine patterns. Thus the fixed length encoding cannot achieve a sufficiently high compression rate. On the other hand, a variable length encoding method can achieve efficient compression while guaranteeing sufficient image quality. The variable length encoding generates codes of variable length depending on the image, and empirically provides an encoding rate of 2–4 bit/pixel, including the luminance and color information and guaranteeing the image quality. In this case, however, it is not possible to guarantee the total number of images recordable per recording medium, because the total amount of codes varies according to the image. Also if the capacity of the recording medium is limited, the image may not be recordable on the recording medium.
Consequently, such variable length encoding method, if employed in a recording apparatus, results in a significant inconvenience as the user is unable to recognize, in advance, the number of images still recordable on the recording medium.
As explained in the foregoing, a system employing fixed length encoding has been unable to guarantee the image quality, while a system employing variable length encoding has been unable to guarantee the number of recordable images. Thus either system has been inconvenient for the user.